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Filippo Berto - One of the best experts on this subject based on the ideXlab platform.
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averaged strain energy density criterion to predict ductile failure of u notched al 6061 t6 plates under mixed mode loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: A R Torabi, Filippo Berto, A. Campagnolo, J AkbardoostAbstract:Abstract The well-known Averaged Strain Energy Density (ASED) criterion, which is basically a brittle fracture criterion, is employed in conjunction with the Equivalent Material Concept (EMC) to predict the experimental failure loads of some U-notched ductile Al 6061-T6 plates reported in the literature under mixed mode I/II loading. While the EMC-ASED criterion does not claim that it is able to predict the fracture plane, the growth path of the crack emanating from the notch border, etc.; it is shown to be successful in predicting the load-carrying capacity (LCC) of the U-notched Al 6061-T6 plates, that fail by the Large-Scale Yielding (LSY) regime, without performing time-consuming and complex elastic-plastic analyses.
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numerical simulation of prestrain history effect on ductile crack growth in mismatched welded joints
Fatigue & Fracture of Engineering Materials & Structures, 2017Co-Authors: Wei Song, Filippo Berto, Xuesong Liu, H FangAbstract:Pipe reeling may lead to plastic pre-deformation (prestrain) around existing cracks in components; therefore, investigating whether this process accelerates or counteracts ductile crack growth, especially for strength mismatched welded joints, is warranted. This study focused on the effect of prestrain history on ductile crack growth in mismatched welded joints. A single-edge-notched tension specimen was selected for numerical study, and the crack was assumed to have existed before a prestrain history was applied. Crack growth resistance curves for plane strain and mode I crack growth under Large-Scale Yielding conditions have been computed using the complete Gurson model. Meanwhile, symmetrical and non-symmetrical prestrain cycle modes with different loading levels were applied to the overmatched specimens. The outcome demonstrated that the mismatch ratio (the ratio between the yield stress of the weld metal and base metal) showed a significant effect on fracture resistance regardless of the stage at which the prestrain cycle loading was located. By contrast, the processing of the crack growth was weakened by the increase of prestrain values, and the symmetrical prestrain cycle resulted in greater plastic damage than the non-symmetrical prestrain cycle did. However, the initial crack length had a non-significant effect on the ductile fracture considering the prestrain and mismatch effects.
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ductile failure prediction of thin notched aluminum plates subjected to combined tension shear loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: A R Torabi, Filippo Berto, S M J RazaviAbstract:Abstract The main goal of the present research is to check the suitability of the combined Equivalent Material Concept-Averaged Strain Energy Density (ASED) failure criterion, called EMC-ASED, in predicting the load-carrying capacity (LCC) of notched aluminum plates subjected to mixed mode I/II loading. For this purpose, first, a set of experimental results on the LCC of thin V-notched rectangular Al 7075-T6 plates, that fail by Large-Scale Yielding (LSY) regime, are taken from the open literature. Then, Al 7075-T6, which is a ductile material, is equated with an equivalent linear-elastic isotropic material by means of the EMC. Finally, the EMC is linked to the well-known ASED criterion to predict the LCC of the notched Al 7075-T6 plates. It is revealed that the experimental results could successfully be predicted by means of the combined EMC-ASED criterion without requiring complex and time-consuming elastic-plastic failure analyses.
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a successful combination of the equivalent material concept and the averaged strain energy density criterion for predicting crack initiation from blunt v notches in ductile aluminum plates under mixed mode loading
Physical Mesomechanics, 2016Co-Authors: A R Torabi, Filippo Berto, A. CampagnoloAbstract:Crack initiation from blunt V-notch borders in ductile A16061-T6 plates is investigated experimentally and theoretically under mixed mode I/II loading. Experimental observations with naked eye during loading indicated Large plastic deformations around the notch tip at the onset of crack initiation, demonstrating Large-Scale Yielding failure regime for the aluminum plates. To theoretically predict the experimentally obtained value of the maximum load that each plate could sustain, i.e. the load-carrying capacity, without performing elastic-plastic failure analyses, the equivalent material concept (EMC) is combined with a well-known brittle fracture criterion, namely the averaged strain energy density (ASED) criterion. It is shown that the combined EMC-ASED criterion could successfully predict the experimental results for various V-notch angles and radii.
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some considerations on the j integral under elastic plastic conditions for materials obeying a ramberg osgood law
Physical Mesomechanics, 2015Co-Authors: Pasquale Gallo, Filippo BertoAbstract:Among the approaches available for structural analysis, the J-integral has received an excellent feedback as a fracture parameter under elastic-plastic conditions. In the literature and dealing with the crack case, it is proposed to evaluate the J-integral as a sum of elastic and plastic contributions. However, some uncertainties arise when applying this method to a Ramberg-Osgood law, especially under Large Scale Yielding conditions.
P Lazzarin - One of the best experts on this subject based on the ideXlab platform.
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fracture behaviour of notched round bars made of pmma subjected to torsion at room temperature
Engineering Fracture Mechanics, 2012Co-Authors: Filippo Berto, P Lazzarin, M Elices, Michele ZappalortoAbstract:Abstract The first part of the paper gives an account of more than 70 new fracture tests on notched specimens made of polymethyl-methacrylate. All static tests are carried out at room temperature under torsion loading conditions. Semi-circular notches as well as U- and V-notches (with an opening angle equal to 120°) are considered, with a root radius ranging from 0.1 to 7.0 mm. Plots of torque loads versus twist angles are recorded varying the notch root radius and the notch depth. In all cases static failure occurs under Large Scale Yielding conditions. Such results can help in evaluating numerical and theoretical models of the fracture of notched components under mode III loading. The second part of the paper deals with a discussion on the experimental results and different approaches are applied to the new data. The notched specimens during the torsion tests present a substantial plastic behaviour and the influence of the effective resistant net area is found to be the predominant parameter with respect to the notch shape (i.e. notch opening angle and tip radius). A non-conventional application of the strain energy density is carried out showing a good agreement between experimental results and theoretical fracture assessments and it is used to justify the link between nominal and local fracture approaches.
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strain energy based evaluations of plastic notch stress intensity factors at pointed v notches under tension
Engineering Fracture Mechanics, 2011Co-Authors: Michele Zappalorto, P LazzarinAbstract:Abstract An analytical study is carried out on the existing link between elastic and plastic notch stress intensity factors at pointed V-notches in plates under tension. The frame is developed on the basis of the elastic and plastic energy concentration factors of the notch defined here as the ratio between the local and the nominal strain energy densities. The link varies under plane stress and plane strain conditions. The local strain energy density is evaluated over a control volume drawn by the energy contour lines ahead of the notch and allows plastic notch stress intensity factors to be predicted on the basis of an ideally linear elastic analysis, both under small and Large Scale Yielding.
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Plastic notch stress intensity factors for pointed V-notches under antiplane shear loading
International Journal of Fracture, 2008Co-Authors: P Lazzarin, Michele ZappalortoAbstract:The paper deals with a work-hardening, elastic–plastic, stress analysis of pointed V-notches under antiplane shear deformation loading both under small and Large Scale Yielding. Stress and strain field intensities are expressed in terms of plastic Notch Stress Intensity Factors, which are analytically linked to the corresponding linear elastic ones under small Scale Yielding. The near tip stress and strain fields are then used to give closed-form expressions for the Strain Energy Density over a circular sector surrounding the notch tip, and for the J -integral parameter, both as a function of the relevant plastic NSIFs, these expressions being valid both under small and Large Scale Yielding.
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control volumes and strain energy density under small and Large Scale Yielding due to tension and torsion loading
Fatigue & Fracture of Engineering Materials & Structures, 2008Co-Authors: P Lazzarin, Filippo BertoAbstract:In the recent literature some researchers proposed the use of the mean value of the Strain Energy Density (SED) over a well-defined control volume for static and fatigue strength assessment of components weakened by sharp V-shaped notches. In those papers the SED was expressed in terms of Notch Stress Intensity Factors (NSIFs), whose accurate evaluation needs a very fine mesh when based on local stress determined along the notch bisector. This contribution shows that when the material behaviour is ideally linear elastic or obeys a power hardening law, the mean value of the SED over the control volume can also be precisely determined from a coarse mesh. This result is of interest in the practical application of the SED approach to real components. Eventually, NSIFs can be evaluated a posteriori, just on the basis of the local SED. While discussing some results from elastic-plastic analyses carried out on a V-notched plate under tension loading and on a V-notched round bar under torsion, the different roles played by local and Large Scale Yielding are highlighted. The result is used here to provide a justification for the different slopes, 3.0 and 5.0, reported by Eurocode 3 and other Standards in force for welded details subjected to tensile or shear stresses, respectively.
A R Torabi - One of the best experts on this subject based on the ideXlab platform.
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j integral expression for mixed mode i ii ductile failure prediction of u notched al 6061 t6 plates under Large Scale Yielding regime
Engineering Fracture Mechanics, 2018Co-Authors: H R Majidi, A R Torabi, M E GolmakaniAbstract:Abstract The main purpose of the present research is to check if the Equivalent Material Concept (EMC) is capable of being combined with the J-integral failure criterion to form a new ductile failure model, called EMC-J criterion, to predict the load-carrying capacity (LCC) of U-notched aluminum plates under mixed mode I/II loading. To achieve this purpose, first, a set of experimental results on LCC of some tested U-notched Al 6061-T6 rectangular specimens, failed by Large-Scale Yielding (LSY) regime, are taken from the recent literature. Due to the elastic–plastic behavior of the tested Al 6061-T6, EMC is utilized to avoid complex and time-consuming non-linear failure analyses for LCC predictions. Then, a new combined ductile failure model is proposed in which J-integral criterion, as a well-established brittle fracture criterion, is combined with EMC to predict theoretically the experimental results of the tested U-notched aluminum plates. Finally, it is shown that EMC-J criterion can predict the experimental results well.
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Tensile failure prediction of U-notched plates under moderate-Scale and Large-Scale Yielding regimes
Elsevier, 2018Co-Authors: A R Torabi, Berto Filippo, Razavi, Seyed Mohammad JavadAbstract:The main goal of the present research is to check if the recently published experimental results on tensile load-carrying capacity (LCC) of ductile U-notched Al 7075-T6 and Al 6061-T6 plates could successfully be predicted by means of combining the Equivalent Material Concept (EMC) with the Averaged Strain Energy Density (ASED) criterion, which is fundamentally a brittle fracture criterion. By using the two main material properties, namely the fracture toughness and the tensile strength of the equivalent material, which is extracted from the EMC, the maximum load that each notched plate could sustain is predicted by means of the combined EMC-ASED criterion. It is revealed that the EMC-ASED criterion is capable of predicting well the LCC of both aluminum plates, independent of the level of ductility of materials and the size of plastic region around the notch at crack initiation instance.submittedVersionThis is a submitted manuscript of an article published by Elsevier Ltd in Theoretical and applied fracture mechanics, 12 July 2017
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averaged strain energy density criterion to predict ductile failure of u notched al 6061 t6 plates under mixed mode loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: A R Torabi, Filippo Berto, A. Campagnolo, J AkbardoostAbstract:Abstract The well-known Averaged Strain Energy Density (ASED) criterion, which is basically a brittle fracture criterion, is employed in conjunction with the Equivalent Material Concept (EMC) to predict the experimental failure loads of some U-notched ductile Al 6061-T6 plates reported in the literature under mixed mode I/II loading. While the EMC-ASED criterion does not claim that it is able to predict the fracture plane, the growth path of the crack emanating from the notch border, etc.; it is shown to be successful in predicting the load-carrying capacity (LCC) of the U-notched Al 6061-T6 plates, that fail by the Large-Scale Yielding (LSY) regime, without performing time-consuming and complex elastic-plastic analyses.
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ductile failure prediction of thin notched aluminum plates subjected to combined tension shear loading
Theoretical and Applied Fracture Mechanics, 2017Co-Authors: A R Torabi, Filippo Berto, S M J RazaviAbstract:Abstract The main goal of the present research is to check the suitability of the combined Equivalent Material Concept-Averaged Strain Energy Density (ASED) failure criterion, called EMC-ASED, in predicting the load-carrying capacity (LCC) of notched aluminum plates subjected to mixed mode I/II loading. For this purpose, first, a set of experimental results on the LCC of thin V-notched rectangular Al 7075-T6 plates, that fail by Large-Scale Yielding (LSY) regime, are taken from the open literature. Then, Al 7075-T6, which is a ductile material, is equated with an equivalent linear-elastic isotropic material by means of the EMC. Finally, the EMC is linked to the well-known ASED criterion to predict the LCC of the notched Al 7075-T6 plates. It is revealed that the experimental results could successfully be predicted by means of the combined EMC-ASED criterion without requiring complex and time-consuming elastic-plastic failure analyses.
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Large-Scale Yielding Failure Prediction of Notched Ductile Plates by Means of the Linear Elastic Notch Fracture Mechanics
Strength of Materials, 2017Co-Authors: A R Torabi, A. Campagnolo, F. BertoAbstract:The main goal of this research is to propose a failure criterion based on the linear elastic notch fracture mechanics (LENFM) for predicting tensile crack initiation from a blunt V-notch, encountering Large plasticity at the notch vicinity. First, some most recently published experimental results on tensile failure of V-notched ductile aluminum plates are briefly described. Then, with the aim to avoid complex and time-consuming elastic-plastic analyses, the equivalent material concept (EMC) is employed together with a LENFM-based fracture criterion, namely the averaged strain energy density (ASED) criterion, for predicting the load-carrying capacity of the V-notched aluminum plates. A very good agreement is shown to exist between the experimental results and theoretical predictions of the EMC-ASED criterion.
Wolfgang Brocks - One of the best experts on this subject based on the ideXlab platform.
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quantification of constraint effects in elastic plastic crack front fields
Journal of The Mechanics and Physics of Solids, 1998Co-Authors: Huang Yuan, Wolfgang BrocksAbstract:In-plane and out-of-plane constraint effects on crack tip stress fields under both small-Scale and Large-Scale Yielding conditions are studied by means of three-dimensional numerical analyses of boundary layer models and of finite size specimens, M(T) and SE(B), respectively. It is shown that the ratio of the plastic zone size over the panel thickness, rpt, plays a key role in formation of the crack-tip fields, particularly the outof-plane stress components. For a vanishingly small plastic zone around the crack tip the stress fields are dominated by the plane strain solution. With increase of the applied loads, i.e. increasing the plastic zone size, the stress fields develop towards the plane stress state. Characterization of “constraint effects” in terms of Q-stress is investigated. The “second term” in the near tip stress field, which is defined as the difference between the full three-dimensional stress fields and the plane strain reference solution, appears to depend on the distance to the tip and to the free surface of the specimen. Hence, the whole three-dimensional crack front fields cannot be correctly described by a two-parameter formulation as the load increases. However, a unique linear relationship between Q and the hydrostatic stress was found in all three-dimensional crack front fields.
Gregory G Deierlein - One of the best experts on this subject based on the ideXlab platform.
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integration of an adaptive cohesive zone and continuum ductile fracture model to simulate crack propagation in steel structures
Engineering Fracture Mechanics, 2021Co-Authors: Vincente Pericoli, Amit Kanvinde, Xai Lao, Andy Ziccarelli, Gregory G DeierleinAbstract:Abstract Damage mechanics continuum criteria have been shown to provide an effective alternative to conventional fracture mechanics parameters to simulate ductile crack initiation in mild steel under Large Scale Yielding and variable stress states. In this study, a damage mechanics initiation criterion, called the Stress Weighted Damage Model, is extended to simulate ductile crack propagation through an Adaptive Cohesive Zone model. The proposed approach regularizes the crack tip singularity using features of conventional cohesive zone methods, while adaptively updating the traction separation relationship to model crack propagation based on the continuum damage criterion. The proposed model is implemented in the finite element platform WARP3D and demonstrated using a set of fourteen coupon Scale fracture experiments of two structural steels. The tests include Circumferentially Notched Tensile bars and sharp-cracked Compact Tension specimens, where the response is represented by load-deformation response and J-R curves, respectively. Comparisons with test results demonstrate that the combined Stress Weighted Damage Model and Adaptive Cohesive Zone approach can accurately simulate crack propagation with consistent mesh convergence. Examples are included to contrast the proposed model capabilities with a conventional (stress-based) Cohesive Zone model and the Gurson-Tvergaard model.
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local cyclic void growth criteria for ductile fracture initiation in steel structures under Large Scale plasticity
2011Co-Authors: Gregory G Deierlein, Amit Kanvinde, Andrew T Myers, B V FellAbstract:Fracture is often the controlling limit state in steel structures, sometimes with catastrophic consequences. As evidenced by recent structural failures, such as the I-35 bridge collapse in Minnesota, in the United States, and the fractures in steel connections during the 1994 Northridge (USA) and 1995 Kobe (Japan) earthquakes, fracture occurs in connections or regions of geometrical discontinuities and material heterogeneities, such as welds. Fracture and fatigue mechanics are highly developed sciences, with widespread application in the mechanical, aerospace and automobile industries. However, traditional fracture and fatigue mechanics are ill-suited for direct application in the context of steel structures in civil construction, for two reasons. First, traditional fracture mechanics is well-suited for characterizing fracture ahead of a sharp crack tip, where only minimal Yielding is present. Typically, fracture in civil structures initiates ahead of a blunt stress raiser, and in the presence of Large Scale Yielding. Thus, more fundamental, micromechanics-based approaches must be developed or adapted for characterizing fracture in these conditions. Second, fatigue-induced fracture in civil structures often occurs under seismic loading. Unlike high-cycle fatigue experienced by bridges under vehicular loads (which involves millions of cycles of low stress amplitude), seismic fatigue in structures typically involves five to twenty cycles of extraordinarily Large amplitude (on the order of several times the yield strain). Termed Ultra Low Cycle Fatigue (or ULCF), this type of fatigue is of specific interest to civil/earthquake engineers, and special models must be developed to characterize the mechanisms (e.g. microvoid growth and collapse) that control this type of fatigue.
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prediction of ductile fracture in steel connections using smcs criterion
Journal of Structural Engineering-asce, 2006Co-Authors: Gregory G Deierlein, Amit Kanvinde, W M ChiAbstract:Conventional fracture mechanics approaches have limited capabilities to accurately predict fracture under conditions of Large Scale Yielding or in complex geometries where there are no significant pre-existing flaws. Such conditions are found, for example, in welded steel moment connections that meet stringent detailing and quality assurance requirements for seismic design that have been imposed in response to damage caused by the Northridge earthquake. The stress modified critical strain (SMCS) criterion provides an alternative approach for modeling ductile crack initiation by relating the fundamental process of void initiation, growth, and coalescence to macroscopic stresses and strains, obtained using detailed finite element models. The material-specific parameters of the SMCS model are calibrated for mild A572 Grade 50 steel using a series of notched tensile tests and fractographic data. Accuracy of the SMCS criterion is demonstrated for specimens with a range of triaxial constraint conditions, including both sharp-crack fracture specimens and blunt-notch specimens, the latter being examples of cases where conventional fracture mechanics approaches would not apply. The SMCS model is then applied in a practical demonstration to relate data from idealized pull-plate tests to the fracture resistance of beam–column moment connections.
